Diving Heart Rate Development in Postnatal Harbour Seals,Phoca vitulina

Abstract

Harbour seals, Phoca vitulina, dive from birth, providing a means of mapping the development of the diving response, and so our objective was to investigate the postpartum development of diving bradycardia. The study was conducted May-July 2000 and 2001 in the St. Lawrence River Estuary (48 degrees 41'N, 68 degrees 01'W). Both depth and heart rate (HR) were remotely recorded during 86,931 dives (ages 2-42 d, n = 15) and only depth for an additional 20,300 dives (combined data covered newborn to 60 d, n = 20). The mean dive depth and mean dive durations were conservative during nursing (2.1 +/- 0.1 m and 0.57 +/- 0.01 min, range = 0-30.9 m and 0-5.9 min, respectively). The HR of neonatal pups during submersion was bimodal, but as days passed, the milder of the two diving HRs disappeared from their diving HR record. By 15 d of age, most of the dive time was spent at the lower diving bradycardia rate. Additionally, this study shows that pups are born with the ability to maintain the lower, more fully developed dive bradycardia during focused diving but do not do so during shorter routine dives.

Rapid maturation of the muscle biochemistry that supports diving in Pacific walruses (Odobenus rosmarus divergens)

“…Harbor seal: 4 week nursing (Reeves et al, 1992), swim and dive at birth (Greaves et al, 2005); hooded seal: 4 day nursing (Reeves et al, 1992), 1 month PWF (Bowen et al, 1987); gray seal: 17 day nursing, 4 week PWF (Reeves et al, 1992); harp seal: 12 day nursing (Reeves et al, 1992), 5-6 week PWF (Sivertsen, 1941); Northern elephant seal: 28 day nursing, 2 months PWF (Reeves et al, 1992); California sea lion: 4-8 months, but frequently >1 year nursing (Reeves et al, 1992); Australian sea lion: at least 1 year nursing (Reeves et al, 1992); Australian fur seal: at least 1 year, rarely 2 year nursing (Reeves et al, 1992); Steller sea lion: 1, 2 and sometimes 3 year nursing (Reeves et al, 1992).…”

“…Differences in diving ability at this stage are associated with differences in body size because, by weaning, the blood oxygen stores of walruses are mature (S.R.N., unpublished), and it is likely that the muscle oxygen store is mature, based on the observation that the longissimus dorsi myoglobin content was already 79% of adult levels by 3 months post-partum (Table 1). Although there are no published accounts of the diving behaviors of immature walruses for comparison, studies on other pinnipeds have demonstrated shorter dive durations, shallower dive depths and a lower percentage of time spent diving by immature seals compared with adult conspecifics (Thorson, 1993;Lydersen and Hammill, 1993;Lydersen et al, 1994;Horning and Trillmich, 1997;McCafferty et al, 1998;Bowen et al, 1999;Burns, 1999;Greaves et al, 2005;Fowler et al, 2006;Rehberg and Burns, 2008). The dive durations of immature pinnipeds increase with age as body size increases (Kooyman et al, 1983;Lydersen and Hammill, 1993;Thorson, 1993;Lydersen et al, 1994;Burns and Castellini, 1996;Burns et al, 1998;Horning and Trillmich, 1997;Burns et al, 1998;Costa et al, 1998;McCafferty et al, 1998;Burns, 1999), and these ontogenetic differences in diving capacity have been associated with inter-age class variations in diet (Bowen et al, 1999;Field et al, 2007;Jeglinski et al, 2012).…”

Development of aerobic and anaerobic metabolism in cardiac and skeletal muscles from harp and hooded seals

“…The ability for young pups to regulate heart rate during dives emerges in utero, as fetal heart rates decline following maternal bradycardia (Bacon et al, 1985;Liggins et al, 1980), and although not fully mature, harbor seal pups demonstrate significant bradycardia during long dives, even at a very young age (Greaves et al, 2005). Despite this, the hearts of young seals are not mature at birth.…”

“…Second, young seals born in arctic environments rely on high rates of metabolic heat production to meet thermoregulatory demands, and therefore have very high metabolic rates (Blix and Steen, 1979;Ostadal et al, 1999). Conversely, immature ability to reduce diving blood flow and heart rate during apnea and diving may favor maintenance of cardiac glycolytic abilities (Greaves et al, 2005;Kodde et al, 2007). However, immature cardiac O 2 stores, enzyme levels and fuel-use patterns could limit the heart's ability to function during dives, and therefore impact diving and foraging activities of young pups.…”

Implantation of subcutaneous heart rate data loggers in southern elephant seals (Mirounga leonina)

“…Implantation of subcutaneous electrodes to measure heart rate has previously been carried out in both otariid and phocid species (Otariidae and Phocidae; McPhee et al 2003;Greaves et al 2005) with the limitation that electrodes had to be wired externally to loggers and glued to the hair. Moreover, externally glued devices can be unreliable because they are prone to falling off as animals move or moult.…”